Diagnostic-Code: smtp; 550 SC-001 (SNT0-MC3-F39) Unfortunately, messages from
IP weren't sent. Please contact your Internet service provider
since part of their network is on our block list. You can also refer your
provider to Troubleshooting.

550 SC-001 Mail rejected by Windows Live Hotmail for policy reasons. Reasons for rejection may be related to content with spam-like characteristics or IP/domain reputation. If you are not an email/network admin please contact your Email/Internet Service Provider for help.

Originally Posted by wooby

Any idea how to proceed to fix this?

This isn't a Zimbra specific problem. If your server sends spam you will, most likely, get on a block list and you need to get yourself removed. This is a question that needs to be addressed to your ISP (see the error message quote above) or you contact Hotmail.

Thanks for the support
Pires, What all measures did u do to fix spam problem?
I have filled their form and it is more than 1 week now and from their support nothing clearcut was provided as when this block can be removed etc...